A hybrid powertrain apparatus that uses a planetary gear set and two motor generators together with an engine may function as a continuously variable transmission, electrically operated by controlling a speed of the motor generator without a separate transmission. Also, by controlling the speed of the motor generator, the hybrid powertrain apparatus may implement a motor mode, an engine mode, a hybrid mode, and a regenerative braking mode.
In the hybrid powertrain apparatus, an on/off control may be performed on the engine as necessary, which may increase fuel efficiency. Also, use of a frictional brake may be minimized in order to increase regenerative braking efficiency.
A structure widely applied to a hybrid electric vehicle powertrain using two motor generators may be an input split type structure in which one of the two motor generators is fixably connected to an output axis directly.
A powertrain in such structure may provide a maximum efficiency at a transmission ratio forming a mechanical point at which a speed of the other motor generator not connected directly to the output axis. On this basis, when the transmission ratio increases or decreases on this basis, the efficiency may decrease. Also, degradation in the efficiency in a case in which the transmission ratio decreases may be radically increased in comparison to a case in which the transmission ratio increases. That is, as the transmission ratio decreases over the mechanical point, for example, as a difference in speed increases, the efficiency of the powertrain may be radically decreased.
Another structure widely applied to a hybrid electric vehicle powertrain using two motor generators may be a compound split structure in which the two motor generators are not connected directly to an output axis or an input axis but connected to different rotary elements of a planetary gear device.
Korean Patent Application No. 2008-0096396 filed on Oct. 1, 2008 discloses “hybrid power train of vehicle.”